What sets custom orthotics apart from over-the-counter orthotics is how well it is shaped to the patient’s feet. In order to create a perfect fit, custom orthotics require a negative cast of the patient’s foot to create a mold. This mold is then used to form the shape of the orthotic device that matches the shape and contour of the patient's foot completely.
Casting a mold of the patient’s foot is an absolute necessity for any correction or accommodation to be made. The accuracy of the mold to the shape of the patient’s foot is a major factor determining patient comfort and the effectiveness of the custom-fabricated orthotic.
A LinkedIn poll in a global group of Podiatrists found 3D scanning to be the most commonly used, followed by Plaster Casting and Impression Foam.
While doctors may favor one casting method over the others, experienced podiatrists and pedorthists need to be familiar with the advantages and disadvantages of all the available options. This article will go through the pros and cons for the 3 main methods of casting the foot as well as different tips for each method to get the best results for custom orthotics.
Plaster Casting
The classic and original method to get the impression of the patient’s foot, plaster casting is often considered the "gold standard” of impression methods. The process involves wrapping wet plaster strips around a patient’s foot as it’s held in a non-weight-bearing neutral position to create a plaster “slipper” that captures a three-dimensional shape of the foot structure and position.
Once the plaster hardens, the slipper is taken off the foot and sent to the orthotics lab. At the lab, more plaster is poured into the slipper to create a positive mold of the foot that is then used in manufacturing the custom orthotic.
The positioning of the foot is vital to create a quality negative cast. For best results, the plaster impression needs to be done in a non-weight bearing position with the midtarsal joint fully locked and the foot in subtalar neutral position. Foot plantarflexion or dorsiflexion can cause the cast to be inaccurate. Ensure that your plaster cast has appropriate depth, defined arch, and no air pockets.
The plaster cast is particularly useful when you are designing functional foot orthotics.
The goal of Plaster casting is to improve the biomechanical function of the foot. It is used to create a device that controls the foot during stance and gait. This helps to counteract excessive motion of the foot.
This method is very accurate, but the process can be messy and time-consuming. It takes patience and skill from the doctor and requires the patient to hold their position for an extended time. Plaster casts can be quite fragile and will dry out or crack over time. Doctors also need to consider costs of packing and shipping the casts, and risk casts being damaged or lost in the mail.
3D Scanning Technology
Modern technology now allows us to take 3D scans of patient feet. When 3D scanning, the patient’s foot is placed on the scanner and then digitally analyzed at the push of a button. Clinical scanners can capture high-quality details of the patients’ feet that are then converted to positive molds. Digital scans can be stored indefinitely and no longer require doctors to ship molds through the mail. No more damage in the mail or storage problems!
Although more convenient than plaster and foam, 3D scanners generally come at a high price starting around $1,200-$2,500 and ranging all the way up to $15,000 or more. Licensing the software can cost extra cost and companies may charge a fee per scan or require yearly contracts. Another thing to keep in mind is that some pressure plate scanners claim to be 3D, but in reality only takes a 2D Scan. Flatbed scanners that lack the infrared hardware to do true 3D scans can only mimic its by estimating arch height and foot shape by analyzing shadows and extrapolating details.
The latest 3D orthotic scanning technology comes in the form of Structure iPad 3D scanner. Doctors can place the patient's foot into the proper position and take a real-time scan from different angles to capture a full 3D image. The Structure scanner is cheaper than other 3D scanners while still creating very accurate casts and also being portable, fast, and convenient for doctors to use. Requires very little training to be able to use it to take reliable scans.
Structure scanners take real 3D scans that are unique to the individual. It does not reference a library or database of existing foot shapes to cut down on production time. The scans taken by the Structure are accurate down to the micrometer and create very precise models of the foot.
Foam Impression Casting
Using impression foam is a bit newer than plaster casting and quite popular. When taking a foam casting, patients are seated with their feet in neutral position. The Doctor then presses their feet gently into the foam while keeping equal pressure on the heel and ball of the foot to ensure an accurate impression.
Orthotics made from foam impressions are often designed to relieve pain in a specific area of the foot. The semi-weight-bearing cast can capture the foot’s natural fat pad expansion. This can be used to determine what areas need special accommodations so that the device is comfortable.
Impression foam is the method of choice when you are making accommodative foot molds.
Impression foam casting has the obvious advantages of being both faster and cleaner. The entire process is very quick and creates very little mess. However, foam is more inaccurate than plaster casting and has a higher deviation range. The casting process can be difficult to master and perfect. Uneven pressure or a wrong angle of impression can cause unexpected results in the positive mold. Foam is also more likely than plaster to receive damage or fall apart in the mail.
Conclusion
All of the casting methods mentioned in this article can be successful if they are performed properly. Never limit yourself to one casting method only! Being able to accurately use multiple casting methods can help doctors adjust to different situations they may encounter depending on the needs or limitations of their patients. For instance:
The patient can't sit or lay down in a certain way.
The patient cannot hold their feet in a certain position for a long time.
Feet with certain deformities or sensitivities.
Medical plans only insure orthotics made using a certain casting method.
The patient needs the orthotics very quickly.
Doctors should put the interest of the patient first by continually practicing and improving their ability to make a good cast. The custom orthotic can only be as good as the cast used to make it. A poor cast can cause a good diagnosis to be useless in improving the patient's foot health and even do more harm than good.
Here at Forward Motion, we accept all methods of casting! We are a fully custom brace and orthotics lab that does not cut corners in creating the perfect device. Each device is made by hand and pressed to a cast using PRX shells and the highest quality materials.
Equipped with the latest technology and more than 20 years of experience in building custom orthotics, there is nothing our team doesn't know how to handle. Learn more about Forward Motion Medical and what we have to offer your practice. Reach out to one of our specialists for a free consultation today!
